Prioritize low vulnerability sites for maintaining or enhancing carbon stocks

Tree mortality from drought, pests and pathogens, fire, windthrow, or other natural disturbances are important causes of carbon loss across forest ecosystems. Sites with characteristics that reduce disturbance frequency or severity, or lower the vulnerability to carbon loss when these disturbances occur, may provide high value for maintaining or enhancing carbon stocks as climatic and biological stressors intensify. Characteristics that lower vulnerability to carbon loss from disturbance may include: (1) high canopy cover or advanced regeneration of species with wide temperature or moisture tolerances, (2) site hydrology or soil fertility that reduces drought or nutrient limitation impacts to forest productivity, or (3) enhanced species or structural diversity that may lower vulnerability or enhance recovery from impacts from pests or pathogens. Maintaining higher carbon stocks on sites with these characteristics that impart greater resistance or resilience to disturbance may provide greater benefit from carbon storage at landscape scales, similar to how sites resistant to climate stressors may provide the best chance for retaining habitat for at-risk species. Additionally, sites may be prioritized for management actions that augment existing characteristics important for resistance to carbon loss or resilience for regaining carbon when disturbances do occur.

Ecosystem carbon density varies spatially across forest and community types due to many factors, such as differences in topography, hydrology, soils, stand age, and disturbance and management history and how these elements influence plant community composition and carbon flux processes. Sites may have high carbon stock densities from either enhanced carbon inputs or conditions that reduce the loss of carbon. High carbon inputs to a site can result from greater productivity of vegetation, high densities of aboveground biomass, or translocation of carbon from adjacent sites, such as soil deposition in floodplains. Additionally, sites may have high carbon densities from reduced carbon losses, such as hydrologic conditions that result in saturated soil conditions limited decomposition and that cause the formation of organic soils. When managing forest ecosystems for carbon, identifying sites containing high carbon densities may be a priority for management in order to retain existing forest carbon stocks. A changing climate is expected to impact sites important for carbon stocks in different ways, depending on vulnerability of the carbon stocks or flux processes to climatic or biological stressors that are expected to intensify.